Processes for the production of ionically-modified polyisocyanate polyaddition products containing urethane and/or urea groups are known and are described, for example, in the following literature references:
DT-PS No. 880,485, DT-AS No. 1,044,404, US-PS No. 3,036,998, PA1 DT-PS No. 1,178,586, DT-PS No. 1,184,946, DT-AS No. 1,237,306, PA1 DT-AS No. 1,495,745, DT-OS No. 1,595,602, DT-OS No. 1,770,068, PA1 DT-OS No. 2,019,324, DT-OS No. 2,035,732, DT-OS No. 2,446,440, PA1 DT-OS No. 2,345,256, DT-OS No. 2,345,257, DT-OS No. 2,427,274, PA1 US-PS No. 3,479,310, U.S. Pat. No. 3,686,108, and Angewandte Chemie 82, 35 (1970). PA1 (a) organic polyisocyanates, optionally together with organic monoisocyanates; with PA1 (b) organic compounds containing at least two isocyanate-reactive groups in the context of the isocyanate addition reaction, optionally in the presence of organic compounds containing one isocyanate-reactive group in the context of the isocyanate addition reaction; compounds containing ionic groups and/or groups which may be converted into ionic groups being used as component (a) and/or (b), characterized in that the compounds containing ionic groups or groups convertible into ionic groups which are used in accordance with the present invention are both: PA1 R represents hydrogen, an aliphatic hydrocarbon radical containing from 1 to 4 carbon atoms or a phenyl radical; PA1 X.sup..sym. represents an alkali metal cation or an optionally substituted ammonium group; PA1 n and m each represents the same or different number of from 0 to 30; PA1 o and p each represents 0 or 1; and PA1 q represents an integer of from 0 to 2. PA1 (1) the (potential) ionic groups are incorporated in the prepolymer by means of suitable (potentially) ionically modified diols; PA1 (2) the (potential) ionic groups are incorporated in the polyaddition product by means of suitable modified amines containing two primary and/or secondary amino groups; PA1 (3) the (potential) anionic or cationic groups are incorporated by the subsequent modification of a polyaddition product containing (potential) cationic or (potential) anionic groups by means of a modifying agent containing free NCO-groups and (potential) anionic or (potential) cationic groups, provision having to be made to ensure that the polyaddition product to be modified contains groups reactive to NCO-groups. It is possible in this way to synthesize polyaddition products in which relatively long, exclusively anionically modified segments are attached to relatively long, exclusively cationically modified segments.
The processes described in these literature references are based on the principle of incorporating ionic groups in a macromolecular chain of a polyurethane-polyurea molecule by means of certain diols introduced into the prepolymer or by means of modified amines acting as chain-extenders for the prepolymers of which each contains at least two terminal NCO-functions. The continuous phase of the known polyurethane dispersions is either water, water-organic solvent in admixture or a pure organic medium, for example a solvent or a polyether or polyester polyol. Standard commercial-grade ionic dispersions are either anionic or cationic dispersions having all the known advantages and disadvantages of the respective ionic groups. Thus, cationic dispersions, for example, have excellent adhesion properties on a variety of different materials, but show relatively low electrolyte and storage stability by comparison with anionic dispersions. Now, it would be of considerable interest to combine the desirable properties of both differently charged systems. There has been no shortage of attempts in this direction.
The most obvious approach to combining the advantageous properties inherent in the two different systems, for example by mixing aqueous dispersions of anionic polyurethanes with aqueous dispersions of cationic polyurethanes, is frustrated by the incompatibility thereof which is mentioned, for example, in DT-OS No. 1,237,306, in DT-OS No. 1,570,602 and in DT-OS No. 2,141,807. It is only possible by using a water-miscible organic solvent, in which some of the solid constituents are soluble, that it is possible in some cases to form a staole system of separately produced cationic and anionic dispersions (DT-OS No. 2,427,247).
It is also known that polyurethanes may be ionically cross-linked by forming an ionic cross-linking system, which, in the case of aqueous polyurethane dispersions, is obtained by inner salt formation between groups capable of salt formation, such as tertiary nitrogen atoms incorporated in a macromolecular chain and free acid groups (DT-AS No. 1,237,306; GB-PS No. 1,076,688; DT-OS No. 1,495,847). As might be expected, this cross-linking effect increases the strength and elasticity of the corresponding end products.
There are also processes for producing polyurethanes having betaine structures which may either be left as such or converted, by reaction with inorganic or organic bases, into salts of polyurethanes having anionic properties or even by reaction with quaternizing agents or acid salt-formers, according to requirements, into salts of polyurethanes having cationic properties (DT-AS No. 1,237,306; DT-OS No. 2,237,114; DT-OS No. 2,536,678; US-PS No. 3,903,032; US-PS No. 3,997,490 and Angewandte Chemie 82, 53 et seq (1970).
It is not possible to obtain the required combination of properties using the ionic polyurethanes containing differently charged ion centers, preferably dispersed in water, which are described in the above literature references. The reason for this would appear to be the intensive interaction of the differently charged ion groups within the betaine structure which partly mask the properties associated with the type of ion. In general, a solution to this problem is regarded as basically impossible because, for example, the stable formation combination of cationic and anionic aqueous dispersions itself encounters insurmountable difficulties and may only be achieved in some cases with the assistance of water-compatible organic solvents.
However, it has now surprisingly been found that it is quite possible to synthesize ionic, non-foamed urethane and/or urea group-containing polyisocyanate polyaddition products which contain both cationic and also anionic groups chemically bound into the same molecule of said polyisocyanate polyaddition products, which are soluble or dispersible in water and/or organic solvents or dispersants and which also combine the known advantages of known anionic and cationic polyurethanes. The polyaddition products which have been discovered in accordance with the present invention are neither ionically cross-linked products nor betaine-like systems; instead they are genuine ampholytes whose properties are determined both by the anionic and also by the cationic groups. Contrary to all expectations, it has also been found that, although these ampholytes according to the present invention are hydrophilic to the extent required for dispersion in water, they are nevertheless so hydrophobic after application that they are distinguished from films of analogous, purely cationic or purely anionic dispersions by the particularly low degree of swelling thereof in water. In this respect, they also differ in particular from films of betaine-containing dispersions which are in fact inferior in the resistance to water thereof to films of anionic or cationic dispersions. Surprisingly, the polyaddition products according to the present invention are also far more suitable than, for example, dispersion mixtures of separately produced anionic and cationic products containing dimethyl formamide, for the coagulation process according to DT-OS No. 1,270,276; DT-OS No. 1,694,171; DT-OS No. 2,345,256 or DT-OS No. 2,427,274, because they have a far less adverse effect upon the technically important operation of washing out the organic solvent than the homogeneous dispersions of the prior art. The organic solvent, for example dimethyl formamide, may be washed out substantially quantitatively using significantly less water in a single washing operation, which is not possible with coagulation auxiliaries of above mentioned dispersion mixtures.
In addition, aqueous dispersions of the polyaddition products according to the present invention show excellent adhesion on a variety of different materials, such as glass, metal, plastics, textiles and leather, by virtue of the presence therein of cationic groups. At the same time, the electrolyte stability thereof is several times higher than that of analogous, purely cationic dispersions by virtue of the anionic group content thereof.